Interventricular dysynchrony is a condition where the right and left ventricles fail to contract in phase. In a normal heart, both ventricles beat together and are effectively “synchronized.” When the ventricles are dyssynchronous, there is a lack of coordinated mechanical activity of the ventricles. This contributes to the evolution of ventricular dysfunction and symptomatic congestive heart failure. Biventricular pacing, a form of cardiac resynchronization therapy (CRT), is an approved modality for treating ventricular failure when interventricular dysynchrony is present and has been shown to improve survival as well as symptoms in patients with congestive heart failure. Response to CRT, however, is variable and, in the past, has been difficult to predict. For example, studies have shown that over 30 percent of patients receiving CRT may not respond to the treatment.
Based on the foregoing, accurate detection of interventricular dysynchrony is not well established. This may be in part due to insufficient characterization of interventricular dyssynchrony by current diagnostic techniques. For example, quantitative detection methods have been based oil data from electrocardiography (EKG) or tissue Doppler echocardiography (echo) tests. For example, selection of patients for CRT has been based on EKG measurements of QRS duration (≧130 ms) and ejection fraction (≦35%). However, EKG data is only a gross estimate of disordered electical and mechanical activation of the ventricles. As for the echo test, it is difficult to administer (especially for the right ventricle) because the operator must locate an acoustic window within which the selected ventricle can be detected by the echo probe. Also, the echo test only captures displacement and velocity information for a small target area on the inner wall of the selected ventricle. Processing the echo data is time intensive. Nevertheless, the results from echo tests suggest that EKG tests are too insensitive and inconclusive. In other words, some patients that appear to exhibit interventricular dyssynchrony in the echo test are not diagnosed as such from EKG results.
Medical imaging techologies (e.g., cardiac magnetic resonance imaging (MRI)) capable of capturing the cardiac cycle have been used to qualitatively diagnose interventricular dyssynchrony through observation of motion sequences showing operation of the ventricles over the cardiac cycle. However, this is a subjective test and requires the experience and expertise of a cardiologist. Nevertheless, this qualitative technique also suggests that EKG tests are too insensitive and inconclusive.
Information related to attempts to address these problems can be found, for example, in PCT Patent Application Publication Number WO 2006/042039 and U.S. Pat. Nos. 6,978,184 and 7,041,061. However, each one of these references requires insertion of a medical instrument (e.g., catheter) or implantation of a medical device (e.g., pacemaker, CRT device, etc.) in the patient in order to test for dyssynchrony. Based at least on the foregoing, there is a need for an improved method and apparatus for detecting interventricular dyssynchrony.